Ligaments are specialized connective soft tissues which connect different organs or tissues and attach bone to bone. In the latter case, ligaments provide stability to joints by being flexible enough to allow natural movement of the bones yet also are strong and inextensible to prevent resistance to applied forces. Tendons connect muscle to bone and are capable of withstanding tension. In addition, tendons passively modulate forces during locomotion, providing additional stability with no active work. Their elastic properties allow tendons to store and recover energy at high efficiency. In tendons and ligaments, bundles of collagen fibers are embedded in a connecting matrix made of proteoglycans components. These bundles of collagen fibers provide the load carrying elements. In tendons, the collagen fibers are arranged in nearly parallel formation, thus enabling them to withstand high unidirectional loads. In ligaments, the collagen fibers are arranged in a less parallel formation, thereby enabling them to withstand predominant tensile stresses in one direction and smaller stresses in other directions.
Every year, hundreds of thousands of people sprain, tear, or rupture ligaments in particular in the knee, shoulder, and ankle or suffer from injuries to tendons of the upper and lower extremities, in particular in the shoulder, knee, foot, and ankle. One such ligament often affected by these type of injuries is the anterior cruciate ligament (ACL) of the knee. The ACL serves as a primary stabilizer of anterior tibial translation and as a secondary stabilizer of valgus-varus knee angulation, and is often susceptible to rupture or tear resulting from a flexion-rotation-valgus force associated with sports injuries and traffic accidents. Ruptures or tears often result in: severe limitations in mobility; pain and discomfort; and an inability to participate in sports and exercise. More than 200,000 people in the U.S. alone tear or rupture their ACL each year, leading to costs of approximately $3 billion for ACL reconstructive surgery and extensive rehabilitation.
It is widely known that the ACL has poor healing capabilities. Total surgical replacement and reconstruction are required when the ACL suffers a significant tear or rupture resulting in joint instability. The most common practice is to reconstruct a torn ACL by substituting the torn ligament with the patient's own tissue, also known as an autograft. Other options for substitute ligaments include donor tissues from another organism, also known as allografts, as well as synthetic grafts. However, there are various problems associated with these treatments.
Surgeons have considered ligament constructs comprising collagen fibers, biodegradable polymers and composites thereof. Collagen scaffolds for ACL reconstruction seeded with fibroblasts from ACL and skin are described for example in the international patent application WO 95/2550. U.S. Patent Application No. 20020123805 by Murray, et al. describes the use of a three-dimensional scaffold composition which includes an inductive core made of collagen or other material, for repairing a ruptured anterior cruciate ligament (ACL) and a method for attaching the composition to the ruptured anterior cruciate ligament (See also U.S. Patent Application No. 20040059416). WO 2007/087353 discloses three-dimensional scaffolds for repairing torn or raptured ligaments. The scaffold may be made of protein, and may be pretreated with a repair material such as a hydrogel or collagen. U.S. Patent Application No. 20080031923 by Murray, et al. describes preparation of a collagen gel and a collagen-MATRIGEL™ gel which is applied to a torn ligament for repair of the ligament. These collagen matrices are mostly monocomponent devices.
A number of multicomponent ligament prosthesis have been described (see, e.g. U.S. Pat. Nos. 3,797,047; 4,187,558; 4,483,023, 4,610,688 and 4,792,336). U.S. Pat. No. 4,792,336 discloses a device with an absorbable component comprising a glycolic or lactic acid ester linkage, and the remainder of the device comprising a non-absorbable component. The device includes a plurality of fibers comprising the absorbable component which can be used as a flat braid in the repair of a ligament or tendon. The required tensile strength is obtained by increasing the final braid denier. U.S. Pat. No. 5,061,283 discloses a bicomponent device comprising polyethylene terepthalate and a polyester/polyether block copolymer for use in ligament repair. U.S. Pat. No. 5,263,984 describes prosthetic ligament which is a composite of two densities of bioresorbable filaments. However, there is still need in the art for a method of ligament and tendon repair that enhances cell ingrowth and metaplastic transformation of the graft tissue to obtain a functional strong neo-ligament/-tendon.